Clinical experience with a programmable pacemaker.

As part of a study to evaluate a new programmable pacemaker, 15 patients received lithium-powered R-wave inhibited, unipolar pulse-generators (CPI Model 0505). Five were initial implants (Group I) and 10 were pulse generator replacements (Group II). The follow-up period ranged from 1 to 18 months (mean 11 months). There were 5 deaths unrelated to the pacemaker. Three instances of pacemaker failure were identified and were characterized by a sudden loss of pacemaker output. THe malfunction, traced to a 10 kHz timing crystal, has been corrected in subsequently manufactured pulse-generators. In 11 patients, the pacemakers were programmed at a pulse width which was twice the threshold determined at 3 months. Four were programmed at 0.1 ms, three at 0.2 ms and four at 0.4 ms. Although no complications were seen in patients programmed at 0.1 ms pulse width, it might be advisable to leave pacemakers at 0.2 ms or greater for chronic pacing in patients with a pulse width threshold at 0.05 mg.